For ink jet recording heads in which part of pressure generating chambers communicating with nozzle orifices for ejecting ink droplets are constituted of a vibration plate and in which the vibration plate is deformed by piezoelectric elements to apply pressure to ink in the pressure generating chambers and thereby to eject ink droplets from the nozzle orifices, two types of ink jet recording heads are in practical use. One uses a longitudinal vibration-mode piezoelectric actuator, which expands and contracts in the axial direction of a piezoelectric element. The other uses a flexural vibration-mode piezoelectric actuator.
In the former type, the capacity of a pressure generating chamber can be changed by bringing an end surface of a piezoelectric element into contact with a vibration plate. A head suitable for high-density printing can be manufactured. However, there is a problem that the manufacturing process is complex for the following reason: this type requires a difficult process of cutting piezoelectric elements into a comb-like shape so as to match the piezoelectric elements with the arrangement pitch of nozzle orifices, and also work of fixing the cut piezoelectric elements while positioning them to the pressure generating chambers.
On the other hand, in the latter type, piezoelectric elements can be formed on a vibration plate by a relatively easy process of adhering a green sheet of a piezoelectric material in accordance with the shapes of pressure generating chambers and baking the green sheet. However, there is a problem that a certain area is needed because of the utilization of flexural vibration and that high-density arrangement is difficult.
Meanwhile, in order to eliminate the disadvantage of the latter recording head, a recording head has been proposed in which a uniform piezoelectric material layer is formed over the entire surface of a vibration plate by deposition technology and in which piezoelectric elements are independently formed for respective pressure generating chambers by cutting the piezoelectric material layer into shapes corresponding to the pressure generating chambers by lithography (for example, refer to Japanese Unexamined Patent Publication No. Hei 5(1993)-286131 (FIGS. 1 to 4)).
Such ink jet recording heads include one having a structure which has a passage-forming substrate and a joint plate joined to the piezoelectric element side of the passage-forming substrate. The passage-forming substrate is provided with at least two rows of pressure generating chambers communicating with nozzle orifices. On the joint plate, a driving IC for driving piezoelectric elements is mounted. In this structure, the driving IC is mounted in an approximately central portion of the joint plate, i.e., in a region corresponding to a region between the rows of the pressure generating chambers. The driving IC and lead wires led from the respective piezoelectric elements are electrically connected by wire-bonding through penetrated holes which are respectively formed along both sides of the driving IC on the joint plate (for example, refer to Japanese Unexamined Patent Publication No. 2003-136734 (FIGS. 1 and 2)).
In such a known ink jet recording head, the manufacturing cost can be kept relatively low because two rows of piezoelectric elements are driven by one driving IC. However, since the penetrated holes are respectively formed on both sides of the driving IC, the areas of the passage-forming substrate and the joint plate need to be made relatively large, and it is difficult to miniaturize the head. In particular, when the pressure generating chambers are arranged at high density, there is a problem that regions for forming a plurality of penetrated holes are difficult to ensure and that the size of a head increases. Note that, of course, such problems exist not only in ink jet recording heads for ejecting ink but also in other liquid jet heads for ejecting liquid droplets other than ink.